The present invention generally relates to extrusion processes and apparatuses therefor. More specifically, the present invention is concerned with processes and apparatuses for extruding chemical functional additives used in making disposable items, such, for example, as paper toweling, napkins, toilet tissue, facial tissue, etc.
Extrusion dies for depositing an extrudable fluid onto a substrate are known in the art. Dies of a type generally known in the art as a coat-hanger die are described, for example, in the following U.S. Pat. No. 4,043,739 issued on Aug. 23, 1997 to Appel and assigned to Kimberly-Clark Corporation; U.S. Pat. No. 4,372,739 issued on Feb. 8, 1983 to Vetter et al. and assigned to Rxc3x6m GmbH of Darmstadt, Germany; U.S. Pat. No. 5,234,330 issued on Aug. 10,1993 to Billow et al. and assigned to Eastman Kodak Company; U.S. Pat. No. 5,494,429 issued on Feb. 27, 1996 to Wilson et al. and assigned to Extrusion Dies, Inc. Several other types of extrusion apparatuses are disclosed, for example, in the following U.S. Pat. No.5,607,726 issued on Mar. 1997 to Flattery et al. and assigned to E. D. du Pont de Nemours and Company; U.S. Pat. No. 5,522,931 issued to Iwashita et al. on Jun. 4, 1996 and assigned to Konica Corporation of Japan; U.S. Pat. No. 5,740,963 issued to Riney on Apr. 21, 1998 and assigned to Nordson Corporation; U.S. Pat. No. 5,511,962 issued to Lippert and assigned to Extrusion Dies, Inc.
Extrusion dies are frequently used in dusty environments. One of the concerns relating to extrusion dies of prior art has been plugging of a die""s discharge mouth, i. e., the outlet through which the extrudable fluid exits the extrusion die. In papermaking, for example, some paper webs tend to be particularly prone to release surface fibers. A dust comprising primarily papermaking fibers may cause contamination of a chemical functional additive, such as, for example, a topical tissue softener, which is routinely deposited onto the paper web. Other common contaminants may include degradation product of the extrudable fluid itself, which particularly may occur in stagnant areas around the walls of the extrusion die. Build up of these degradation products can form over a period of time, harden and eventually separate from the walls of the die, thereby becoming a contaminant. More generally, particulate soil, sand, dirt, and grit tend to become airborne in the vicinity of the extrusion operation and settle into the supply of the extrudable fluid feeding the extrusion die.
If the chemical functional softener, for example, is deposited onto a substrate by extrusion, the contaminants, which have found their way into the functional additive being extruded, may plug the discharge outlet of the extrusion die. A process of cleaning of the extrusion dies is usually costly, for it involves stoppage of a production line and/or a substantial effort. The cleaning may be further complicated in extrusion dies designed to extrude very thin layers of extrudates and therefore comprising the discharge mouths having very small, in the range of 0.0002-0.00450 inches, dimensions requiring maintenance of high-precision tolerances. As the cross-sectional area of the discharge mouth decreases, the propensity of internal clogging of the die increases. Capillary-sized discharge mouths are especially susceptible to clogging.
The disclosures of commonly-assigned patent applications Ser. No. 9/258,497 filed on Feb. 29, 1999; and Ser. No. 09/377,661 filed on Aug. 19, 1999, both applications filed in the name of the present inventor, are incorporated herein by reference.
It is believed that a dynamic flow inducer of the present invention, comprising at least one rotatable element disposed within the discharge mouth of an extrusion die, can beneficially mitigate, and even eliminate the problem of plugging of the discharge mouth. Accordingly, the present invention provides a novel dynamic flow inducer. The present invention also advantageously provides a novel extrusion apparatus comprising a discharge mouth having a dynamic flow inducer therein that retards the accumulation of contaminant and thereby prevents clogging of the extrusion apparatus""s discharge moth. The present invention also provides an advantage of an extrusion process which substantially eliminates plugging of the discharge mouth of the extrusion apparatus.
Other objects, features, and advantages of the present invention will be readily apparent from the following description taken in conjunction with accompanying drawings, although variations and permutations may be had without departing from the spirit and scope of the disclosure.
The present invention provides an extrusion die comprising a supply port and a distribution channel in fluid communication with the supply port. The distribution channel terminates with at least one discharge mouth having a passage cross-section therethrough. The discharge mouth comprises an entry orifice, an exit orifice, a discharge distance therebetween, and a dynamic flow inducer. The dynamic flow inducer comprises a movable member and is positioned such as to form the narrowest section of the discharge mouth. In some embodiments, the dynamic flow inducer partially obstructs the flow of the fluid being discharged. The movement of the dynamic flow inducer substantially decreases and even negates the possibility that contaminants in the fluid will accumulate and clog the discharge mouth.
In one embodiment of the present invention, the dynamic flow inducer comprises a bar that is rotated in a direction concurrent with the flow. In another embodiment, the dynamic flow inducer comprises a bar that is translated along its longitudinal axis. The dynamic flow inducer may comprise a plurality of the rotatable bars. For example, in one embodiment, two rotatable bars are disposed on mutually opposite sides of the discharge mouth. The rotatable bars may have grooves thereon of differential shapes (such as, for example, circular and rectangular), and differential configurations (such as, for example, radial and helical).
In some embodiments, the rotatable bar or bars may be disposed substantially perpendicular to the general direction of the flow of the extrudable fluid within the discharge mouth. However, it is contemplated in the present invention that the rotatable bar or bars can be disposed such as to form an acute angle or angles between the bar""s axis of rotation and the general direction of the flow of the extrudable fluid.
The rotatable bar(s) can be structured to move in a direction different from that of the extrudable fluid, for example in the direction transverse to the flow of the extrudable fluid. In one embodiment, the rotatable bar is biased within the discharge mouth of the extrusion die to move transversely thereby widening the passage cross section of the discharge mouth.
The present invention further provides a process for extruding an extrudable fluid used in making a disposable paper product. The process comprises the steps of providing an extrudable fluid, providing an extrusion die equipped with the dynamic flow inducer of the present invention, and extruding the fluid with the extrusion die. The present invention also teaches that internal clogging of the extrusion die can be prevented by applying a reverse (or back) pressure to the fluid in the extrusion die, thereby displacing larger contaminants which tend to accumulate at the entry orifice of the discharge mouth.
The present invention also teaches a process for depositing a chemical functional additive onto a web substrate. The process comprises the steps of providing a web substrate; providing an extrusion die having a dynamic flow inducer of the present invention; providing the chemical functional additive selected from the group consisting of softeners, emulsions, emollients, lotions, topical medicines, soaps, anti-microbial and anti-bacterial agents, moisturizers, coatings, inks and dyes, and binders; extruding the functional additive with the extrusion die while facilitating passage of at least some of the contaminants contained in the functional additive, and depositing the functional additive extrudate onto the web substrate. In a preferred embodiment, the web substrate is moving in a machine direction.